The anterior pituitary is composed of several cell types, each responsible for the production of specific hormones. Each hormone secreting cells is defined by the activation of its respective hormone genes in a temporally and spatially regulated manner. Recent development in cytochemistry and molecular biology have provided various aspects of human pituitary adenomas, i.e., functional differentiation and classification. The molecular factors that determine hormone production have now been identified as transcription factors. Many novel transcription factors that play a role in anterior pituitary development are implicated. In this review, we focus on the transcriptional factors roles on functional differentiation of the pituitary cells and adenomas and the contribution of cytochemistry and recent development in molecular biological techniques.